Watercraft construction

ABSTRACT

A hydrofoil has an elongated hull of a predetermined first volume and is provided with a bottom wall and a longitudinally extending center keel. Two or more stabilizing elements are provided on the respective lateral sides of the keel, flanking the same, and defining between themselves beneath the bottom wall of the hull at least one air channel which extends longitudinally of the hull and whose volume is equal to between substantially one-fifteenth and one-third of the volume of the hull itself. Various other features are also disclosed.

United States Patent 1 Boden Sept. 25, 1973 1 WATERCRAFT CONSTRUCTION[76] Inventor: Wilhelm Boden, Kreis Eckemfoerde Schlei, Kopperby/ueberKappeln, Germany [22] Filed: Dec. 22, 1970 [21] Appl. No.: 100,673

[30] Foreign Application Priority Data Dec. 23,1969 Norway 5087 [52] US.Cl ll4/66.5 R [51] Int. Cl B63!) l/38 [58] Field of Search 114/66.5 R,67 A,

[56] References Cited UNITED STATES PATENTS Apel 114/665 R 3,148,6529/1964 Canaui 114/6615 S Primary ExaminerGeorge E. A. Halvosa AssistantExaminer-Stuart M. Goldstein AttorneyMichael S. Striker [57] ABSTRACT Ahydrofoil has an elongated hull of a predetermined first volume and isprovided with a bottom wall and a longitudinally extending center keel,Two or more stabilizing elements are provided on the respective lateralsides of the keel, flanking the same, and defining between themselvesbeneath the bottom Wall of the hull at least one air channel whichextends longitudinally of the hull and whose volume is equal to betweensubstantially one-fifteenth and one-third of the volume of the hullitself. Various other features are also disclosed.

62 Claims, 10 Drawing Figures PATENTEU SEP 2 51975 SHEET 1 (IF 3 FIGJINVENTORQ l/Eaneon 130020 BY: 1 /00! #h'll Pmmvinsimm 3.760.756

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INVENTOR KIM/Ivan 600:0

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INVENTOR 0140061! 800cm 5 lion 1. 1H.

ATTORNEY 1 WA TERCHAW COMM/anon BACKGROUND OF THE INVENTION The presentinvention relates generally to a watercraft, and more particularly to ahydrofoil.

The use of the term hydrofoil as employed herein is intended to beunderstood in the broadest sense in that it includes a skimmer, that isa type of watercraft which skims over the surface or substantially overthe surface of a body of water.

Such hydrofoils are already known. One type, with which the presentinvention is specifically concerned, is provided on the bottom wall ofthe hull at opposite lateral sides of the longitudinal center linesthereof, with stabilizing elements which are arranged symmetrically withreference to the center keel of the hull. The problem with these knownconstructions is that they require a rather significant propulsioneffort, and also that they have a tendency to pitch and roll. This istrue particular at higher speeds.

Attempts have been made in the prior art to avoid these problems byproviding longitudinally extending stabilizing bodies on the bottom wallportion of the hull, such that two sets of these bodies are providedlocated at opposite sides of the longitudinal center line of the hull,with each side being composed of a plurality of stabilizing bodies andwith the individual stabilizing bodies of each set receding in laterallyoutward and upward direction in stepwise manner. This is already anadvantage over earlier constructions in that it makes watercraft of thistype more resistant to the aforementioned problems and more maneuverableat high speed. Whereas these stabilizing bodies are elongated and ofsubstantially planar configuration, another prior-art proposal suggeststhe use of elongated stabilizing bodies which are substantially ofV-shaped cross-section. These begin in the region of the bow of the hulland end in the region of the stern. The longest body of each seteach setis composed of a plurality of bodies of different length-is closest tothe center line of the hull. Here, the stabilizing bodies areconfigurated as displacement or water-displacement bodies which,however, disadvantageously influence the attainment of high speedsbecause they increase the resistance or drag of the ship during movementthereof through the water.

Finally, it is also known in this type of watercraft to provide in theregion of the bow a forwardly projecting plate element the purpose ofwhich is to advantageously influence the gliding or skimming of thecraft. Again, however, experience has shown that this expedient does nothave the desired effect and efiiciency, because the generally curvedconfiguration of the remainder of the craft is not conductive to theskimming motion.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to overcome the aforementioned disadvantages of the art.

A more specific object of the invention is to provide an improvedwatercraft of the type under discussion which is not possessed of theseaforementioned disadvantages.

A concomitant object of the invention is to provide such an improvedwatercraft which has a minimum drag or resistance to movement throughwater.

Another object of the invention is to provide such an improvedwatercraft which converts in a simple and inexpensive as well asreliable manner, and without the aid of auxiliary devices, the densityof the water through which is moves to a lesser density by admixingwater with air, in order to substantially reduce in this manner thesurface friction resistance encountered during movement through thewater.

In pursuance of the above objects, and others which will become apparenthereafter, one feature of the invention resides in a watercraft,particularly in a hydrofoil, which briefly stated comprises an elongatedhull of a predetermined first volume having a bottom wall portion whichis provided with a longitudinally extending center keel. At least twostabilizing elements are provided on this bottom wall portion exteriorlyof the hull and flanking the center keel at opposite lateral sidesthereof. These elements define between themselves beneath and togetherwith the bottom wall portion at least one air channel which extendslongitudinally of the wall and which has a second volume of betweensubstantially one-fifteenth and one-third of the aforementionedpredetermined first volume,

Preferably, the second volume should be one-sixth of the first volume.

The thus-obtained advantageous construction according to the presentinvention is further enhanced by additional features according to thepresent invention. Thus, according to an additional embodiment the topwall of the air channel, which is constituted by a corresponding part ofthe bottom wall portion of the hull, rises from the region of the sterntowards the region of the bow of the hull in such a manner that when thewatercraft is at rest in a body of water, the top wall of the airchannel comes in contact with the water only in the region of the bow ofthe hull.

It is further advantageous according to the present invention that thewidth of the air channel have to the width of the hull (measured belowthe water line) less the width of the hull, a relationship of 1:1 and beat least equal to the total width of the hull measured below thewaterline. However, the width of the air channel can also be somewhatgreater. Thus, if the total width of the hull measured below thewaterline is for instance 3 meters, then the width of the air channelwould be 1.5 meters or perhaps even somewhat greater.

Also, the height of the side walls bounding the air channel measuredover the entire active length, may amount to approximately one-third ofthe width of the air channel itself.

According to a further embodiment of the invention the height of theseside walls is to decrease in the direction from the bow towards thestern of the hull, approximately in correspondence with the inclinationof the bottom wall portion which also is declined in rearward direction,that is from the hull towards the stern. It is assumed for purposes ofthis consideration that the downwardly directed surfaces of the twostabilizing elements which flank the center keel of the hull are to beconsidered as located horizontally for purposes of measurement of theseside walls.

The upright height of these side walls should be at least 15 cm in theregion of the stern. This value may be less only in small ships, such assporting craft or the like, preferably those having a total length ofless than 6 meters.

Also, an embodiment of the invention provides that the totalcross-sectional areas of all stabilizing elementswhich of course act ina buoyant capacity-which are immersed in water when the watercraft is atrest, correspond approximately at least to the crosssectional area ofthe air channel, measured substantially midway between the bow and thestern.

In order to increase and facilitate the whirlingtogether and admixtureof water with the air it is further proposed to providemeans--preferably in the bow region-which effect such admixture at highcruising speed of the watercraft. It is important that the proportion ofair to water in such admixture be as high as possible. Means for thispurpose may be drawn from a wide range of possibilities, for instancethey may be in form of a plate which extends forwardly at an upwardinclination from the bow at an angle of for instance between and 45 andwhich is provided with slots or other apertures. Another possibility isa grid-like metallic or non-metallic element which again preferablyextends forwardly and upwardly at an angle of between for instance 10and 45.

A somewhat similar effect is obtained if there is provided, inaccordance with a further object of the invention, in the region of thebow at least one transverse connecting element which extends across theair channel between the two stabilizing elementsor the two innermoststabilizing elements, if more than two are provided-and which is ofhydrodynamically advantageous configuration. Preferably, such an elementshould extend over at least half the width of the air channel. It can beconnected to only one of the two stabilizing elements, that is it neednot extend from one to the other of the stabilizing elements all the wayacross the air channel. It may be of generally wing-shaped configurationand may even be located outside of the air channel, being mounted at theoutwardly directed sides of the stabilizing elements, or even of thehull itself. In this case there are preferably two such elementsprovided which are arranged symmetricaly with reference to one another.

A further important concept according to the present invention providesthat at least two stabilizing elements project rearwardly beyond thestern of the hull. The projecting portions of these elements may beprovided with a transversely extending plate which connects them, ifdesired.

Important for purposes of the present invention is also that dependingupon the length of the watercraft, the bottom wall portion of the hullis inclined at an angle of between substantially 8 and 20 from the sternto the bow. Here, again, it is assumed for purposes of determining themeasurement that the downwardly directed surfaces of the two stabilizingelements are oriented in horizontal position.

A further and very important concept of the present invention providesthat at least one air supply conduit-- -preferably is ofcircumferentially closed crosssectionextends into the air channel. Thisair supply conduit may have one or more inlets in the region of the bow,laterally on the elongated hull, or at another place, for instance atthe deck or the like. It will have at least one or more outlets whichcommunicate with the air channel at a suitable location, for instance inthe region of its first or leading third, its last or trailing third, orits intermediate third. Preferably the communication will be in theregion of the ceiling of the air channel, but as a general rule thelocation where the outlets or outlet will be provided depends upon adetermination where the incoming medium will have its most advantageousdegree of effectiveness.

According to the invention the outlet opening or openings of the supplyconduit or conduits may be configurated as nozzles, that is they may betapered to slotshaped configuration in order to obtain an improvedeffect. If several air supply conduits are provided, there inletopenings may be distributed to various portions of the hull, forinstance some of them may be located at the deck, some of them at thebow and others in a side wall of the hull. However it is to beunderstood that these inlet openings may also be located at otherportions of the hull than those which have been mentioned, preferablysuch portions which are wetted by water, which means that they can alsobe located at or in the stabilizing elements.

In the region of the outlet opening or openings the air supply conduitmay be so configurated as to project beyond the wall portion of the hullin which the outlet opening or openings will be provided. Thus, tubularportions of the air supply conduit or conduits may project out of therespective wall and at their free ends or in the region of their freeends may have one or more outlet openings which may be simple aperturescorresponding to the cross-section of the tubular portion, or which maybe configurated as slot-shaped or otherwise configurated nozzles. Suchnozzles may be mounted and arranged on the center line or keel of thewatercraft facing rearwardly towards the stern, or they may be inclinedwith reference to this center line at a desired angle. In fact, withreference for instance to the bottom wall portion of the hull theseoutlet openings may be oriented at a desired acute or obtuse angle-withreference to the direction of advancement of the watercraft-and they mayalso be made adjustable so they can be adjusted at the will of a user,preferably but not necessarily during the actual movement of the craft.However the necessary adjustment can be carried out in known manner, forinstance by means of Bowden linkages or the like. For instance, theangular inclination of the outlets may be desired to be different duringstart-up than during cruising speed.

In order to obtain an increased supply of air through the air supplyconduit or conduits, a source of compressed air may be provided, such asa compressed-air bottle, a compressor, or the like. This would forinstance be used when for brief period of times top speeds are to beachieved, at which occasions the source will be connected with the airsupply conduit or conduits.

The air inlet openings of the air supply conduit or conduits may also bemade to be located outwardly away from the respective wall surface wherethey are provided. Thus, again tubular or otherwise configuratedextension portions of the air supply conduit or conduits may projectbeyond such wall surfaces and be provided at or in the region of theirfree ends with the air inlet openings. They may be made telescopable andthe cross-section of the tubular portions may diverge in directiontowards the inlet openings, or putting it conversely, they converge indirection inwardly away from the inlet openings. The inlet openings maybe subdivided into separate apertures if desired and they may also beconfigurated as nozzles. Similarly, the outlet openingsinstead of beingconfigurated as nozzles-may be of convergent cross-section if desired.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic sideview of a watercraft according to the present invention;

FIG. 2 is a front view of the watercraft in FIG. 1, looking towards theright-hand side, and providing a fragmentary enlarged detail view;

FIG. 3 is a view similar to FIG. 2 illustrating a further detail of theinvention;

FIG. 4 is a fragmentary diagrammatic detail view illustrating yetanother concept of the invention;

FIG. 5 is a front view of a detail shown in FIG. 4;

FIG. 6 is a view substantially analagous to that of FIG. 2 illustratingan additional embodiment of the invention;

FIG. 7 is a fragmentary diagrammatic side view of a watercraft accordingto another embodiment of the invention;

FIG. 8 is a diagrammatic view analogous to that of FIG. 2, but on asmaller scale, showing a further embodiment of the invention;

FIG. 9 is a diagrammatic view in explanation of another detail of theinvention; and

FIG. 10 is a fragmentary diagrammatic side view of a portion of awatercraft incorporating still an additional concept of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing indetail it will be seen that the hull of the watercraft as illustrated inFIGS. 1 and 2, for instance, is generally identified with referencecharacter H. The particular configuration of the hull as such is of noimportance for purposes of the present invention, but of course, it isunderstood that in keeping with the specific type of watercraft involvedthe hull will be configurated along lines based upon hydrodynamic andaerodynamic principles which are well known in this field.

The hull H is provided with an air supply conduit 3 which in theillustrated embodiment extends from the bow of the hull H (at theleft-hand side of FIG. I) towards the center of the hull, that issubstantially midway between the bow and the stern which is identifiedat the right-hand side of FIG. 1 with reference numeral 38. At thismidpoint the air supply conduit 3, whose air inlet openings 3' arevisible in FIG. 2, communicates with an air channel 1 which is definedby the bottom wall portion of the hull H and by the innermost pair 4aand 7a of stabilizing and buoyancy elements which are mounted on thebottom wall portion and which flank the longitudinal center line of thehull at opposite lateral sides thereof, to define with the bottom wallportion the longitudinally extending air channel 1. When the watercraftis in a static floating condition, then the bottom wall portion defineswith reference to the surface of the body of water on which it floats asubstan- 6 tially wedge-shaped air filled space 4 which isdiagrammatically illustrated in FIG. 1 and which tapers in the directionfrom the bow towards the stem 38. Depending upon the speed of movementimparted to the watercraft from its static position, and depending uponthe trim of the watercraft, the wedge-shaped space 4 will usually becomelarger, that is it will usually become higher in the region of the bowas the latter lifts out of the water.

According to the present invention this air channel 1 in which thewedge-shaped air cushion 4 is formed, will become filled during forwardmovement of the watercraft in dependence upon the travelling speedthereof-with a medium in form of air-water fog which, due to theadmixture of profuse quantities of air with the water rushing throughthe channel 1, will form a medium of reduced density, thus correspondingto a reduction of the wetted surface area on the hull and resulting in aconcomitant reduction of the surface friction resistance.

The necessary air volume in the channel 1 is obtained, according to thepresent invention, depending upon the travelling speed of the watercraftpartially by the dynamic pressure of the air which is forced into thechannel 1 during forward movement of the watercraft, and partially by asuction effect which develops at the outlet or trailing end of thechannel 1 due to the ejection effect resulting from escape of thewater-air mixture.

FIG. 2 shows that the watercraft illustrated is provided with two setsof stabilizing elements, each set being located at one lateral side ofthe center line of the hull. One of these sets is identified withreference numerals 4a, 5a and 6a, and the elements of the other set areidentified with reference numerals 7a, 8a and 9a. In all cases theelements extend symmetrically with reference to the center line and fromthe region of the bow 3d (see FIG. 2) to the region of the stem 38. Thelongest ones of these elements, namely the elements 4a and 7a, areclosest to the keel and bound with one another the' channel 1.

As seen from the interior of the channel 1, the elements of each set(namely 4a, 5a and 6a, or 7a, 8a and 9a) recede laterally outwardly aswell as upwardly in step-shaped formation as illustrated in the drawing.They are also of different height in laterally outward direction so thatthe respectively outermost elements 6a and 9a are immersed in the waterto the least extent as compared with the elements 5a and 4a on the onehand and the elements 8a and 7a on the other hand. The number ofelements to be used-which theoretically could be two, namely theelements 4a and 7adepends upon the size of the hull. In any case, bythis pro vision the watercraft is given its dynamic trim.

In FIG. 2 the height of the inner side walls bounding the channel 1,that is the inwardly directed surfaces of the elements 4a and 7a, isidentified with the doubleheaded arrow H. According to the inventionthis height H is to be greater in the front region of the hull than thesimilar height h which is indicated in FIG. 1 in the region of the stem11 and which is to be no less than 15 cm. The height H according to thepresent invention should continuously decrease to the height h.

FIG. 3 shows that the combined cross-sectional areas F F F F F and F ofthe elements 40 9a, which becomes immersed beneath the waterline L whenthe watercraft is at rest, corresponds at least approximately to thecross-sectional area F of the channel 1, measured substantially midwayof the hull as indicated by a comparison of the double-headed arrows lwith the double-headed arrows in FIG. 1.

In FIGS. 4 and 5 I have illustrated means for facilitating at highspeedmovement of the watercraft, admixture of the air with the water in orderto efficiently form the air-water fog in the channel 1. Thus, aplate-shaped element 12 may be secured at the bow 13 and may projectforwardly and at an upwardly inclined angle of between substantially and45. It may be located partially below the waterline and may be providedwith longitudinal slots 13 as illustrated in FIG. 5. It can also belocated as indicated by the open-line representation 15 and may beinclined at a different angle as that illustrated, as already pointedout before. Naturally, the slots 13 could be provided with bores orother apretures of various different sizes and configurations, or

the plate 12 may be constructed as a grid or the likef In FIG. 2 I haveillustrated a substantially wingshaped element which may be provided 'inlieu of or in addition to the element 12 of FIGS. 4 and 5, serving thesame purpose. In FIG. 2 the wing-shaped element is identified withreference numeral 16 and is mounted on the inner side of the element 4a,being turnable as indicated by the arrow 17. A similar element 16 mustalso be provided on the inner side of element 7a. It is also possible,however, to provide a single such element which extends from the element4a to the element 7a, being mounted on both of them for turning movementabout a transverse axis in the direction as indicated by the arrow 17.Conversely, however, an element such as the element 16 may also beprovided at the outer sides of, for instance, the stabilizing elements6a or 9a in which case again two such elements must be provided.

If a single element analogous to the element 16 is used, then theconstruction shown in FIG. 6 may be utilized. Here, the element isidentified with reference numeral 18 and is mounted turnably on supports19 provided on the inner sides of the elements 4a and 7a. However, it isclear that the element 18 may also be shorter or somewhat longer thanwhat has been illustrated in FIG. 6 and reference numeral 43 in-FIG. 6shows that it is preferably although not absolutely necessarily providedwith cutouts, apertures or the like.

Returning to FIG. 1 it will be seen that according to a further conceptof the invention the bottom wall portion of the hull and the downwardlydirected surface 21 of the element 70 (and of course also of the element4a) define with one another an angle 20 which should be betweensubstantially 6 and 20, it being assumed again that the surfaces 21 ofelements 4a and 7a are substantially longitudinally oriented.

As FIG. 1 also shows, the outlet end of the air supply conduit 3 (orconduits 3) is identified with reference numeral 22. It, or the severaloutlets 22, may be located as desired, either in the first third of thelength of the channel 1, in the second third or in the third third(compare FIG. 1). If several conduits 3 are provided, one of them mayhave its outlet or outlets communicate with the first third of thechannel, one or more with the second third, and so on. The outletopenings 22 may be configurated, as illustrated for instance in FIG. 7,in form of a nozzle 23 of substantially slot-shaped crosssection. Thismeans that in the region 24 the crosssection of the channel 3 issubstantially circular, but can also be of other configuration, and thendecreases to the nozzle-shaped configuration 23 where the air enters thechannel 1. It is also possible as shown in FIG. 1 to provide forinstance a channel or supply conduit 3a which may for instance have itsopening for inlet or air located at the deck of the watercraft, or atany other suitable location, and whose outlet 25 is located on thestabilizing element 7a, or the element 40. When air enters in thedirection of the arrow 26, then it will exit at 25 below the downwardlydirected surface 21 (compare FIG. 2) and will advance in the directionof the arrow 7 towards the stern of the watercraft, forming beneath thesurface 21 an aircushion.

It is also possible according to an embodiment of the invention, and asshown in FIG. 3, to have the air outlet openings 30 located outside andbeyond the bottom wall 29, in that the conduit is extended to thelocation 25. This is indicated by the broken lines in FIG. 3 and it willbe appreciated that this projecting portion of the conduit will beconfigurated in streamlined shape so as to offer as little resistanceand drag as possible. A similar outlet opening 3b is provided which ishere formed with a telescopic extension 26a which may or may not beconfigurated as a nozzle. A suitable arrangement, as for instance aBowden linkage or the like of known construction, may be provided foradvancing and retracting the extension portion 26a during travel of thewatercraft so that the length of the portion 26a can be selected at willand the point within the channel 1 at which it delivers a stream of aircan similarly be selected freely at the will of an operator, therebyaccommodating this arrangement to the prevailing operating conditions.

In the embodiment of FIG 3 the opening 25 and that of the extensionportion 26a are inclined with reference to the longitudinal center lineof the hull. However, they could also discharge vertically, that is inparallelism with the inner surfaces of the elements 4a and 7a,respectively. Then again, they could also be arranged precisely at or onthe center line.

In FIGS. 1 and 7 I have shown that with reference to the inclination ofthe bottom wall portion 29 from the bow towards the stern of thewatercraft, the channels 3 and 3a are inclined at an acute angle. Thisinclination can, however, be selected as desired and another angle maybe chosen, such as that of a further air supply conduit 30 which isidentified in broken lines in FIG. 1 and which defines an abtuse angleidentified with reference numeral 30. Of course, the outlet openings,such as the outlet opening 31, are directed opposite the direction offorward movement of the watercraft.

In FIG. 7 I have illustrated that portions of the conduits or channels3, 30, etc. may also project beyond the respective wall surface at whichtheir inlets are provided, and their cross section may then divergesuchas in the configuration of the funnel 32 shown in FIG. 7-so that agreater air quantity is scooped into the respective conduits 3, 3a, etc.whereby increased pressure develops in these conduits and more air isejected into the channel 1 or beneath the surfaces 21. Advantageouslythe portion 32 is telescopable and can be retracted or advanced (advanceposition as shown in FIG. 7) and this can preferably be done duringmovement of the watercraft. However, portion 32 can also be of one piecewith the remainder of the respective conduit 3, 3a. As also shown inFIG. 7, the conduits 3, 30 may have more than one outlet opening, suchas the openings 23 and 33. They may of course be located as desired toprovide for instance even distribution of air in the channel 1. It isalso shown in FIG. 7 that it is preferable to arrange a valve member,such as a turnably mounted plate 34 in the conduit 3. A Bowden linkageor similar means is provided for turning the plate 34 about a pivot axisin the direction of the arrow 35, so that the cross-section of therespective conduit (3 .in this case) can be completely closed, partiallyopened or completely opened, whereby the flow of air therethrough can bethrottled at will. In addition a further plate 36 can be mounted in thechannel 1 as shown in FIG. 2. Such a plate should preferably, but notnecessarily, be apertured or be constructed as a gridwork. It has thepurpose to maintain the air as close as possible to the bottom wall ofthe hull, and at the other hand it facilitates the admixture of air withwater.

It is also advantageous according to the present invention that at leasttwo of the stabilizing elements (one each located at opposite lateralsides of the center line of the hull) project beyond the stem 11 andterminate for instance in the region h. For instance they may extend tothe arrows designating reference numeral 20.

The projecting portions of such elements may be connected by aconnecting element as shown in FIG. 8. This may be in form of a platewhich connects the projecting portions 712 and 4b, these designationshaving been chosen to indicate that these are portions of the elements7a and 4a which project beyond the stem 11. The connecting element is inform of a plate-shaped member 38 which extends between and connects theportions 7b and 4b as illustrated. The lower surface 39 of the element38 is not located in a common general plane with the lower surface ofthe bottom wall portion 29 of the hull, but instead is located in asomewhat different plane. However, the surfaces 29 and 39 could also belocated in a common plane that is be located flush, and also the surface39 could be located higher than the surface 29.

It is also advantageous that the air oulet openings such as thoseidentified with reference numerals 23, 33 and the like can be adjustedin their angular-orientation with reference to the elongation of thechannel 1, so that the air which is ejected from these openings willcontact the surface of the water at an angle which can be freelyselected in accordance with prevailing requirements and considerations.

The arrow 40 in FIG. 7 indicates that it is also possible to provide anair inlet opening for the conduit 3 where a compressor or a bottle ofcompressed air or the like can be connected. This may for instance bedesirable if insufficient air enters through the funnel 32 when themotion of the watercraft first begins. In this case air can then i beforcably introduced from the source supplied for this purpose, with theplate 34 being first used to close the cross-section of the conduit 3 inorder to prevent the escape of such air through the inlet opening of theportion 32. Thus, such compressed air fulfills the function withordinarily newly incoming air fulfills which enters during movement ofthe watercraft into the inlet opening or openings of the conduits 3, 30.

Of course, the air outlet opening or openings, such as the oneidentified with reference numeral 33, could also be divergent asindicated at 32 for the inlet open- In FIG. 9 I have illustrated, andthis is also shown in FIG. 1, that the surface 41 of the element 9a (andof course also conversely the same surface of the element 6a) should notrise as strongly towards the bow of the hull, as does the bottom wallportion 29 thereof. This means that the height of the inner walls 42 ofthe elements 7a and 4a increases more rapidly in the direction towardsthe bow than the surface 48 increases in the same direction.

It is also advantageous if the inclination of the bottom wall portion 29is such that no part of this bottom wall portion will become wetted bycontacting the water when the watercraft is at rest in the water.

In the region 42 of the valve at least one hydrodynamically configuratedconnector may be located between and connected to the elements 4a and7a. This connector may be configurated such as the element 16 or as theelement 18 of FIG. 6. It may be made immovable or it may be turnableabout a substantially horizontal pivot axis, and a suitable arrangement,such as a Bowden linkage or the like, may be provided for effecting suchturning even while the watercraft is in motion.

The plate 18 may be provided with the illustrated cutouts 43 in form ofslots, apertures or the like, or it may be provided with projectionsand/or depressions, all having the purpose to facilitating admixture andturbulence of water with air.

It is clear from what has been said and illustrated that the inletopening to the various air supply conduits may be located whereverdesired, for instance also on superstructures or the like, and that theoutlet openings may be provided in the bottom wall portion bounding inpart the channel 1, or at another suitable location as previouslydiscussed.

In FIG. 10 I have shown that a damping element 46 may be provided whichis either stationary or turnable and which may be located at one side ofthe bow (with a similar elements being located at the other nonvisibleside) for damping the movement of the watercraft with reference to thewater through which it advances. Of course, this element 46 may havevarious different configurations and it may for instance also be locatedlower than illustrated so that it is actually located below the bow andprojects laterally to both sides thereof.

In FIG. 8 I have illustrated a keel 46 which according to the presentinvention should reach to above the waterline of the hull in the staticcondition of the watercraft, meaning that at the bow it should extendfar enough upwardly so that in that region it is not contacted by thewater when the craft is not in motion.

Returning to FIG. 2 is it pointed out that according to another conceptof the invention the height of the strips defined by laterally adjacentones of the stabilizing elements, for instance the elements 7a and 8a,or the elements and 9a, and so on, should be greater in the region ofthe bow of the hull than in the region of the stem 38. This distance isidentified with a doubleheaded arrow 46 in FIG. 2 and the concept isalso evident from FIG. 1. It will be noted that the distance of thelines 38 and 39 is greater in the region of the bow than in the regionof the stern and the same is true for the lines 49 and 50.

Finally, it is also pointed out that according to another concept of theinvention the construction of the channel 1, and particularly the widthof the channel 1 should be dependent upon the length of the hull andshould amount to approximately one-sixth of that portion of the lateralsurfaces 42 which are wetted during movement of the watercraft. Duringsuch movement, and as a result of the raising of the bow out of thewater, not the entire length of the surfaces 42 is in the water, butonly perhaps two-thirds of this length. Thus, the width b of the channel1 is to amount to approximately one-sixth of this length as indicated inFIG. 2.

Insofar as any features have been identified as known or conventional,for instance the use of means for making adjustments during movement,such as Bowden linkages or the like, it is not believed necessary todescribe these in detail because they are well known and are expedientwhich will readily and thoroughly offer themselves to those havingordinary skill in the art.

It will be understood that each of the elements de scribed above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in awatercraft, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. In a watercraft, particularly a hydrofoil, in combination, anelongated hull of a predetermined first volume having a waterline and abottom wall portion provided with a longitudinal extending center keel;and at least two stabilizing elements provided on said bottom wallportion exteriorly of said hull and flanking said center keel atopposite lateral sides thereof, said elements defining betweenthemselves beneath and together with said bottom wall portion at leastone airchannel which extends longitudinally of said hull and has asecond volume of between substantially onefifteenth and one-third ofsaid predetermined first volume, the transverse width of said airchannelbeing at least equal to half the transverse width of said hull at thelevel of said waterline, and said stabilizing elements having downwardlydirected bottom faces which are recessed in the form of a plurality ofsteps located under the level of said bottom wall portion and extendingin direction upwardly and outwardly of said hull so as to compensate forthe unsteadying influence of said air-channel.

2. In a watercraft as defined in claim 1 wherein said airchannel has asecond volume of substantially onesixth of said first volume.

3. In a watercraft as defined in claim 1, said stabilizing elements eachhaving an upright inner surface facing the interior of said airchannel,and wherein each of said surfaces has a height which corresponds atleast substantially to one-third of the transverse width of saidairchannel.

4. In a watercraft as defined in claim 1, said watercraft having a bowand a stern; and wherein said bottom wall portion is upwardly inclinedfrom said stern towards said bow such that with said hull stationarysaid bottom wall portion is below said waterline only in the region ofsaid bow.

5. In a watercraft as defined in claim 4, said stabilizing elements eachhaving an upright inner surface facing the interior of and laterallybounding said airchannel; and wherein the height of said surfacesincreases in direction from said stern towards said bow of saidwatercraft.

6. In a watercraft as defined in claim 1, said stabilizing elements eachhaving an upright inner surface facing the interior of and laterallysaid airchannel; and wherein said surfaces each have a height which inthe region of a stern of said watercraft is equal to at least 15 cm.

7. In a watercraft as defined in claim 1, said watercraft having a bow,a stern and said hull being normally submerged to said waterline whenstationary, and said stabilizing elements each having a cross-sectionalarea which is at least in part submerged when said watercraft isstationary; and wherein said airchannel terminates midway between saidbow and said stern.

8. In a watercraft as defined in claim 1; and further comprisingadmixing means for admixing and agitating air and water passing beneathsaid bottom wall during cruising movement of said watercraft.

9. In a watercraft as defined in claim 8, said watercraft having a bow,and said admixing means being provided in the region of said bow.

10. In a watercraft, particularly a hydrofoil, in combination, anelongated hull of a predetermined first volume having a bottom wallportion which is provided with a longitudinally extending center keel;at least two stabilizing elements provided on said bottom wall portionexteriorly of said hull and flanking said center keel at oppositelateral sides thereof, said elements defining between themselves beneathand together with said bottom wall portion at least one airchannel whichextends longitudinally of said hull and has a second volume of betweensubstantially one-fifteenth and onethird of said predetermined firstvolume; and at least one wing-shaped agitator member mounted in saidairchannel and extending transversely of the same.

11. In a watercraft as defined in claim 10, wherein said agitator memberis provided in said air-channel in the region of a stern of saidwatercraft.

12. In a watercraft as defined in claim 1 1; and mounting means mountingsaid agitator member stationarily with reference to said hull.

13. In a watercraft as defined in claim 1 l; and mounting means mountingsaid agitator member for turning movement about an axis extendingtransversely of the elongation of said hull.

14. In a watercraft as defined in claim 10; and mounting means mountingsaid agitator member on one of said stabilizing elements, said agitatormember extending from said one stabilizing element towards but short ofthe other of said stabilizing elements.

15. In a watercraft as defined in claim 14; and further comprising anadditional agitator member mounted on the other of said stabilizingelements and extending towards but short of said one stabilizingelement.

16. In a watercraft as defined in claim 15, wherein said stabilizingelements'are spaced from one another longitudinally of said airchannel.

17. In a watercraft as defined in claim 14; and further comprising anadditional agitator member also mounted on'said one stabilizing elementbut spaced from the first-mentioned agitator member longitudinally ofsaid airchannel, said additional agitator member also extending towardsbut short of said other stabilizing element.

18. In a watercraft as defined in claim 1, said stabilizing elementseach having an inner side facing said airchannel, and an outer side; andfurther comprising at least a pair of wingshaped agitator members eachmounted on the outer side of one of said stabilizing elements andprojecting in direction outwardly therefrom.

19. In a watercraft as defined in claim 14, wherein said airchannel hasa predetermined transverse width; and wherein said agitator memberextends from said one stabilizing'element across at least half of saidpredetermined width.

20. In a watercraft as defined in claim 1, said watercraft having a bowand a stern; and wherein said bottom wall portion is upwardly inclinedin direction from said stern towards said bow at an angle of between 6and with reference to said stabilizing elements.

21. In a watercraft, particularly a hydrofoil, in combination, anelongated hull of a predetermined first volume having a bow, a waterlineand a bottom wall portion provided with a longitudinally extendingcenter keel; at least two stabilizing elements provided on said bottomwall portion exteriorly of said hull and flanking said center keel atopposite lateral sides thereof, said elements defining betweenthemselves beneath and together with said bottom wall portion at leastone airchannel extending longitudinally of said hull and having a secondvolume of between substantially onefifteenth and one-third of saidpredetermined first volume, the transverse width of said airchannelbeing at least equal to half the transverse width of said hull at thelevel of said waterline and said stabilizing elements having downwardlydirected bottom faces which are recessed in the form of aplurality ofsteps located under the level of said bottom wall portion and extendingin direction upwardly as well as outwardly of said hull so as tocompensate for the unsteadying influence of said airchannel; and airsupply conduit meansprovided on said hull and having inlet means facingin direction substantially towards said bow and outlet means at least inpart communicating with said airchannel.

22. In a watercraft as defined in claim 21, said outlet means beingconfigurated as outlet nozzle means.

23. In a watercraft as defined in claim 21, said airchannel having aleading portion, an intermediate portion and a trailing portion as seenwith reference to the direction of forward movement of said watercraft,and wherein said outlet means communicates with at least one of saidportions.

24. In a watercraft as defined in claim 23, wherein said one portion issaid leading portion.

25. In a watercraft as defined in claim 23, wherein said one portion issaid trailing portion.

26. In a watercraft as defined in claim 23, wherein said one portion issaid intermediate portion.

27. In a watercraft as defined in claim 21, said air supply conduitmeans comprising a plurality of air supply conduits each having at leastone inlet and at least one outlet, all of said outlets communicatingwith said airchannel and said inlets being spaced from one another andlocated in different regions of said watercraft.

28. In a watercraft as defined in claim 21, said outlet means comprisingat least two outlets one of which communicates with said airchannel, andthe other of which is provided outside said airchannel at leastsubstantially in the region of the waterline of said watercraft.

29. In a watercraft as defined in claim 21, said outlet means comprisingat least two outlets; and further comprising at least one telescopictubular extension portion telescoped into said air supply conduit meansand extendable and retractable through at least one of said outletswhile said watercraft is in motion.

30. In a watercraft as defined in claim 21, said outlet means comprisingat least two outlets provided laterally of and inclined with referenceto said center keel.

31. In a watercraft as defined in claim 21, said outlet means comprisingat least two outlets provided in and spaced longitudinally of said keel.

32. In a watercraft as defined in claim 21, said outlet means beinginclined at a predetermined angle with reference to said bottom wallportion and to the elongation of said hull.

33. In a watercraft as defined in claim 21, said outlet means beinginclined at a predetermined angle with reference to the elongation ofsaid hull and facing towards the stern of said watercraft.

34. In a watercraft as defined in claim 21, said air supply conduitmeans comprising a main portion and at least one tubular portionprojecting from said main portion beyond said hull and being providedwith said inlet means.

35. In a watercraft as defined in claim 34, said tubular portion havinga passage provided with an inner end communicating with said mainportion and with an outer free end provided .with said inlet means; andwherein said passage has a cross-section which converges in directionfrom said inlet means towards said inner end.

36. In a watercraft as defined in claim 21, said air supply conduitmeans comprising at least two air supply conduits; and wherein at leastone of said air supply conduits comprises at least two conduit brancheseach having at least one outlet.

37. In a watercraft as defined in claim 21, said air supply conduitmeans comprising a plurality of air supply conduits each having at leastone inlet; and wherein all of said inlets are located at leastsubstantially on a common level of said hull.

38. In a watercraft as defined in claim 21, said air supply conduitmeans comprising a plurality of air supply conduits each having at leastone inlet; and wherein said inlets are located on different levels ofsaid hull.

39. In a watercraft as defined in claim 21; further comprising at leastone adjustable throttling element mounted in at least one of saidairchannel and air supply conduit means for throttling the flow of airtherethrough at the will of an operator.

40. In a watercraft as defined in claim 39, wherein said throttlingelement is mounted in said air supply conduit means.

41. In a watercraft as defined in claim 40; and further comprising anadditional throttling element adjustably mounted in said airchannel forthrottling the flow of air through the same at the will of an operator.

42. In a watercraft as defined in claim 41, said additional throttlingelement being a tumable apertured plate.

43. In a watercraft as defined in claim 21, said outlet means comprisingoutlet nozzles mounted for displacement between a plurality of positionsin which they are respectively inclined at different angles withreference to the elongation of said air-channel.

44. In a watercraft as defined in claim 21; and further comprising asource of compressed air connectable with and disconnectable from saidair supply conduit means at the will of a user.

45. In a watercraft as defined in claim 35, wherein said tubular portionis of one piece with said main portion.

46. In a watercraft as defined in claim 21, said air supply conduitmeans comprising at least one air supply conduit having a cross-sectionwhich diverges in direction towards said outlet means.

47. In a watercraft as defined in claim 21, said elements each having adownwardly directed surface which is upwardly inclined in direction fromsaid stern towards said bow at a first angle; and wherein said bottomwall portion is upwardly inclined in direction from said stern towardssaid bow at a second angle which is greater than said first angle.

48. In a watercraft as defined in claim 21, said watercraft having astern; and wherein said bottom wall portion is upwardly inclined fromsaid stern towards said bow such that said bottom wall portion is abovesaid waterline in its entirety.

49. In a watercraft as defined in claim 21, said elements having acombined buoyancy so selected as to float said hull when said watercraftis stationary.

50. In a watercraft as defined in claim 21, said watercraft having astern; and further comprising at least one connecting element extendingbetween and connecting said elements in the region of said bow withinthe confines of said airchannel and having a configuration selected forproviding minimum hydrodynamic drag.

51. In a watercraft as defined in claim 50, wherein said connectingelement is fixed.

52. In a watercraft as defined in claim 50; and further comprisingmounting means mounting said connecting element for pivotal displacementabout an axis extending transversely to the elongation of saidairchannel.

53. In a watercraft as defined in claim 21; and further comprising atleast one motion-damping element provided on said hull and projectinglaterally of the same in the region of said bow.

54. In a watercraft as defined in claim 21, wherein said keel tapersgradually rearwardly of said bow from an inclined to a substantiallyhorizontal orientation, and also tapers transversely of the elongationof said hull at least to the region of the lateral center of gravity ofsaid hull.

55. In a watercraft as defined in claim 21, wherein the height of saidstepped recesses is greater in the region of the bow of said hull thanin the region of the stern of said hull.

56. In a watercraft as defined in claim 55, wherein said heightdecreases continuously in direction from said bow towards said stern ofsaid hull.

57. In a watercraft as defined in claim 21, wherein at cruising speed ofsaid watercraft only a predetermined fraction of the longitudinalextension of said bottom wall portion comes in direct contact with thewater; and wherein said airchannel has a transverse width whichcorresponds substatially to one-sixth of said fraction 58. In awatercraft, particularly in a hydrofoil, in combination, an elongatedhull of a predetermined first volume, said hull having a waterline, abow, a stern and a bottom wall portion extending between said bow andsaid stern and being provided with a longitudinally extending centerkeel; and at least two stabilizing elements provided on said bottom wallportion exteriorly of said hull and flanking said center keel atopposite lateral sides thereof, said elements having respective firstportions defining between themselves beneath and together with saidbottom wall portion at least one airchannel extending longitudinally ofsaid hull and having a second volume of between substantiallyonefifteenth and one-third of said predetermined first volume, andrespective second portions which project longitudinally beyond saidstern by a predetermined extent, the transverse width of saidair-channel being at least equal to half the transverse width of saidhull at the level of said waterline, and said elements further havingdownwardly directed bottom faces which are recessed in the form of aplurality of steps located under the level of said bottom wall portionand extending in direction upwardly as well as outwardly of said hull soas to compensate for the unsteadying influence of said air-channel.

59. In a watercraft as defined in claim 21; and further ocmprising aconnecting plate extending between and connecting said second portionswith one another.

60. In a watercraft as defined in claim 59, said bottom wall portion andsaid connecting plate each having a downwardly directed surface; andwherein said surfaces are located at least substantially in a commonplane.

61. In a watercraft, particularly a hydrofoil, in combination, anelongated hull of a predetermined first volume having a bow and a bottomwall portion which is provided with a longitudinally extending centerkeel; at least two stabilizing elements provided on said bottom wallportion exteriorly of said hull and flanking said center keel atopposite lateral sides thereof, said elements defining betweenthemselves beneath and together with said bottom wall portion at leastone airchannel which extends longitudinally of said hull and has asecond volume of between substantially onefifteenth and one-third ofsaid predetermined first volume; and admixing means mounted in theregion of said bow for admixing and agitating water which passes beneathsaid bottom wall during cruising movement of said watercraft, saidadmixing means comprising an apertured plate projecting forwardly fromsaid bow in the direction of cruising movement of said watercraft at anupward angle of between substantially 10 and 45.

62. In a watercraft, particularly a hydrofoil, in combination, anelongated hull of a predetermined first volume having a bow and a bottomwall portion which is provided with a longitudinally extending centerkeel; at least two stabilizing elements provided on said bottom wallportion exteriorly of said hull and flanking said center keel atopposite lateral sides thereof, said elements defining betweenthemselves beneath and together with said bottom wall portion at leastone airchannel which extends longitudinally of said hull and has aseocnd volume of between substantially onefifteenth and one-third ofsaid predetermined first volume; and admixing means mounted in theregion of said bow for admixing means comprising a grid-shaped

1. In a watercraft, particularly a hydrofoil, in combination, anelongated hull of a predetermined first volume having a waterline and abottom wall portion provided with a longitudinal extending center keel;and at least two stabilizing elements provided on said bottom wallportion exteriorly of said hull and flanking said center keel atopposite lateral sides thereof, said elements defining betweenthemselves beneath and together with said bottom wall portion at leastone airchannel which extends longitudinally of said hull and has asecond volume of between substantially one-fifteenth and one-third ofsaid predetermined first volume, the transverse width of said airchannelbeing at least equal to half the transverse width of said hull at thelevel of said waterline, and said stabilizing elements having downwardlydirected bottom faces which are recessed in the form of a plurality ofsteps located under the level of said bottom wall portion and extendingin direction upwardly and outwardly of said hull so as to compensate forthe unsteadying influence of said air-channel.
 2. In a watercraft asdefined in claim 1 wherein said airchannel has a second volume ofsubstantially one-sixth of said first volume.
 3. In a watercraft asdefined in claim 1, said stabilizing elements each having an uprightinner surface facing the interior of said airchannel, and wherein eachof said surfaces has a height which corresponds at least substantiallyto one-third of the transverse width of said airchannel.
 4. In awatercraft as defined in claim 1, said watercraft having a bow and astern; and wherein said bottom wall portion is upwardly inclined fromsaid stern towards said bow such that with said hull stationary saidbottom wall portion is below said waterline only in the region of saidbow.
 5. In a watercraft as defined in claim 4, said stabilizing elementseach having an upright inner surface facing the interior of andlaterally bounding said air-channel; and wherein the height of Saidsurfaces increases in direction from said stern towards said bow of saidwatercraft.
 6. In a watercraft as defined in claim 1, said stabilizingelements each having an upright inner surface facing the interior of andlaterally said airchannel; and wherein said surfaces each have a heightwhich in the region of a stern of said watercraft is equal to at least15 cm.
 7. In a watercraft as defined in claim 1, said watercraft havinga bow, a stern and said hull being normally submerged to said waterlinewhen stationary, and said stabilizing elements each having across-sectional area which is at least in part submerged when saidwatercraft is stationary; and wherein said airchannel terminates midwaybetween said bow and said stern.
 8. In a watercraft as defined in claim1; and further comprising admixing means for admixing and agitating airand water passing beneath said bottom wall during cruising movement ofsaid watercraft.
 9. In a watercraft as defined in claim 8, saidwatercraft having a bow, and said admixing means being provided in theregion of said bow.
 10. In a watercraft, particularly a hydrofoil, incombination, an elongated hull of a predetermined first volume having abottom wall portion which is provided with a longitudinally extendingcenter keel; at least two stabilizing elements provided on said bottomwall portion exteriorly of said hull and flanking said center keel atopposite lateral sides thereof, said elements defining betweenthemselves beneath and together with said bottom wall portion at leastone airchannel which extends longitudinally of said hull and has asecond volume of between substantially one-fifteenth and one-third ofsaid predetermined first volume; and at least one wing-shaped agitatormember mounted in said airchannel and extending transversely of thesame.
 11. In a watercraft as defined in claim 10, wherein said agitatormember is provided in said air-channel in the region of a stern of saidwatercraft.
 12. In a watercraft as defined in claim 11; and mountingmeans mounting said agitator member stationarily with reference to saidhull.
 13. In a watercraft as defined in claim 11; and mounting meansmounting said agitator member for turning movement about an axisextending transversely of the elongation of said hull.
 14. In awatercraft as defined in claim 10; and mounting means mounting saidagitator member on one of said stabilizing elements, said agitatormember extending from said one stabilizing element towards but short ofthe other of said stabilizing elements.
 15. In a watercraft as definedin claim 14; and further comprising an additional agitator membermounted on the other of said stabilizing elements and extending towardsbut short of said one stabilizing element.
 16. In a watercraft asdefined in claim 15, wherein said stabilizing elements are spaced fromone another longitudinally of said airchannel.
 17. In a watercraft asdefined in claim 14; and further comprising an additional agitatormember also mounted on said one stabilizing element but spaced from thefirst-mentioned agitator member longitudinally of said airchannel, saidadditional agitator member also extending towards but short of saidother stabilizing element.
 18. In a watercraft as defined in claim 1,said stabilizing elements each having an inner side facing saidairchannel, and an outer side; and further comprising at least a pair ofwingshaped agitator members each mounted on the outer side of one ofsaid stabilizing elements and projecting in direction outwardlytherefrom.
 19. In a watercraft as defined in claim 14, wherein saidairchannel has a predetermined transverse width; and wherein saidagitator member extends from said one stabilizing element across atleast half of said predetermined width.
 20. In a watercraft as definedin claim 1, said watercraft having a bow and a stern; and wherein saidbottom wall portion is upwardly inclined in direction from said sterntowards sAid bow at an angle of between 6* and 20* with reference tosaid stabilizing elements.
 21. In a watercraft, particularly ahydrofoil, in combination, an elongated hull of a predetermined firstvolume having a bow, a waterline and a bottom wall portion provided witha longitudinally extending center keel; at least two stabilizingelements provided on said bottom wall portion exteriorly of said hulland flanking said center keel at opposite lateral sides thereof, saidelements defining between themselves beneath and together with saidbottom wall portion at least one air-channel extending longitudinally ofsaid hull and having a second volume of between substantiallyone-fifteenth and one-third of said predetermined first volume, thetransverse width of said airchannel being at least equal to half thetransverse width of said hull at the level of said waterline and saidstabilizing elements having downwardly directed bottom faces which arerecessed in the form of a plurality of steps located under the level ofsaid bottom wall portion and extending in direction upwardly as well asoutwardly of said hull so as to compensate for the unsteadying influenceof said airchannel; and air supply conduit means provided on said hulland having inlet means facing in direction substantially towards saidbow and outlet means at least in part communicating with saidair-channel.
 22. In a watercraft as defined in claim 21, said outletmeans being configurated as outlet nozzle means.
 23. In a watercraft asdefined in claim 21, said airchannel having a leading portion, anintermediate portion and a trailing portion as seen with reference tothe direction of forward movement of said watercraft, and wherein saidoutlet means communicates with at least one of said portions.
 24. In awatercraft as defined in claim 23, wherein said one portion is saidleading portion.
 25. In a watercraft as defined in claim 23, whereinsaid one portion is said trailing portion.
 26. In a watercraft asdefined in claim 23, wherein said one portion is said intermediateportion.
 27. In a watercraft as defined in claim 21, said air supplyconduit means comprising a plurality of air supply conduits each havingat least one inlet and at least one outlet, all of said outletscommunicating with said airchannel and said inlets being spaced from oneanother and located in different regions of said watercraft.
 28. In awatercraft as defined in claim 21, said outlet means comprising at leasttwo outlets one of which communicates with said airchannel, and theother of which is provided outside said airchannel at leastsubstantially in the region of the waterline of said watercraft.
 29. Ina watercraft as defined in claim 21, said outlet means comprising atleast two outlets; and further comprising at least one telescopictubular extension portion telescoped into said air supply conduit meansand extendable and retractable through at least one of said outletswhile said watercraft is in motion.
 30. In a watercraft as defined inclaim 21, said outlet means comprising at least two outlets providedlaterally of and inclined with reference to said center keel.
 31. In awatercraft as defined in claim 21, said outlet means comprising at leasttwo outlets provided in and spaced longitudinally of said keel.
 32. In awatercraft as defined in claim 21, said outlet means being inclined at apredetermined angle with reference to said bottom wall portion and tothe elongation of said hull.
 33. In a watercraft as defined in claim 21,said outlet means being inclined at a predetermined angle with referenceto the elongation of said hull and facing towards the stern of saidwatercraft.
 34. In a watercraft as defined in claim 21, said air supplyconduit means comprising a main portion and at least one tubular portionprojecting from said main portion beyond said hull and being providedwith said inlet means.
 35. In a watercraft as defined in claim 34, saidtubular portion having a passage provided with an inner endcommunicating with said main portion and with an outer free end providedwith said inlet means; and wherein said passage has a cross-sectionwhich converges in direction from said inlet means towards said innerend.
 36. In a watercraft as defined in claim 21, said air supply conduitmeans comprising at least two air supply conduits; and wherein at leastone of said air supply conduits comprises at least two conduit brancheseach having at least one outlet.
 37. In a watercraft as defined in claim21, said air supply conduit means comprising a plurality of air supplyconduits each having at least one inlet; and wherein all of said inletsare located at least substantially on a common level of said hull. 38.In a watercraft as defined in claim 21, said air supply conduit meanscomprising a plurality of air supply conduits each having at least oneinlet; and wherein said inlets are located on different levels of saidhull.
 39. In a watercraft as defined in claim 21; further comprising atleast one adjustable throttling element mounted in at least one of saidairchannel and air supply conduit means for throttling the flow of airtherethrough at the will of an operator.
 40. In a watercraft as definedin claim 39, wherein said throttling element is mounted in said airsupply conduit means.
 41. In a watercraft as defined in claim 40; andfurther comprising an additional throttling element adjustably mountedin said airchannel for throttling the flow of air through the same atthe will of an operator.
 42. In a watercraft as defined in claim 41,said additional throttling element being a turnable apertured plate. 43.In a watercraft as defined in claim 21, said outlet means comprisingoutlet nozzles mounted for displacement between a plurality of positionsin which they are respectively inclined at different angles withreference to the elongation of said air-channel.
 44. In a watercraft asdefined in claim 21; and further comprising a source of compressed airconnectable with and disconnectable from said air supply conduit meansat the will of a user.
 45. In a watercraft as defined in claim 35,wherein said tubular portion is of one piece with said main portion. 46.In a watercraft as defined in claim 21, said air supply conduit meanscomprising at least one air supply conduit having a cross-section whichdiverges in direction towards said outlet means.
 47. In a watercraft asdefined in claim 21, said elements each having a downwardly directedsurface which is upwardly inclined in direction from said stern towardssaid bow at a first angle; and wherein said bottom wall portion isupwardly inclined in direction from said stern towards said bow at asecond angle which is greater than said first angle.
 48. In a watercraftas defined in claim 21, said watercraft having a stern; and wherein saidbottom wall portion is upwardly inclined from said stern towards saidbow such that said bottom wall portion is above said waterline in itsentirety.
 49. In a watercraft as defined in claim 21, said elementshaving a combined buoyancy so selected as to float said hull when saidwatercraft is stationary.
 50. In a watercraft as defined in claim 21,said watercraft having a stern; and further comprising at least oneconnecting element extending between and connecting said elements in theregion of said bow within the confines of said airchannel and having aconfiguration selected for providing minimum hydrodynamic drag.
 51. In awatercraft as defined in claim 50, wherein said connecting element isfixed.
 52. In a watercraft as defined in claim 50; and furthercomprising mounting means mounting said connecting element for pivotaldisplacement about an axis extending transversely to the elongation ofsaid airchannel.
 53. In a watercraft as defined in claim 21; and furthercomprising at least one motion-damping element provided on said hull andprojecting laterally of the same in the region of said bow.
 54. In awatercraft as defined in claim 21, wherein said keel tapers graduallyrearwardly of said bow from an inclined to a substantially horizontalorientation, and also tapers transversely of the elongation of said hullat least to the region of the lateral center of gravity of said hull.55. In a watercraft as defined in claim 21, wherein the height of saidstepped recesses is greater in the region of the bow of said hull thanin the region of the stern of said hull.
 56. In a watercraft as definedin claim 55, wherein said height decreases continuously in directionfrom said bow towards said stern of said hull.
 57. In a watercraft asdefined in claim 21, wherein at cruising speed of said watercraft only apredetermined fraction of the longitudinal extension of said bottom wallportion comes in direct contact with the water; and wherein saidairchannel has a transverse width which corresponds substatially toone-sixth of said fraction
 58. In a watercraft, particularly in ahydrofoil, in combination, an elongated hull of a predetermined firstvolume, said hull having a waterline, a bow, a stern and a bottom wallportion extending between said bow and said stern and being providedwith a longitudinally extending center keel; and at least twostabilizing elements provided on said bottom wall portion exteriorly ofsaid hull and flanking said center keel at opposite lateral sidesthereof, said elements having respective first portions defining betweenthemselves beneath and together with said bottom wall portion at leastone airchannel extending longitudinally of said hull and having a secondvolume of between substantially one-fifteenth and one-third of saidpredetermined first volume, and respective second portions which projectlongitudinally beyond said stern by a predetermined extent, thetransverse width of said air-channel being at least equal to half thetransverse width of said hull at the level of said waterline, and saidelements further having downwardly directed bottom faces which arerecessed in the form of a plurality of steps located under the level ofsaid bottom wall portion and extending in direction upwardly as well asoutwardly of said hull so as to compensate for the unsteadying influenceof said air-channel.
 59. In a watercraft as defined in claim 21; andfurther ocmprising a connecting plate extending between and connectingsaid second portions with one another.
 60. In a watercraft as defined inclaim 59, said bottom wall portion and said connecting plate each havinga downwardly directed surface; and wherein said surfaces are located atleast substantially in a common plane.
 61. In a watercraft, particularlya hydrofoil, in combination, an elongated hull of a predetermined firstvolume having a bow and a bottom wall portion which is provided with alongitudinally extending center keel; at least two stabilizing elementsprovided on said bottom wall portion exteriorly of said hull andflanking said center keel at opposite lateral sides thereof, saidelements defining between themselves beneath and together with saidbottom wall portion at least one airchannel which extends longitudinallyof said hull and has a second volume of between substantiallyone-fifteenth and one-third of said predetermined first volume; andadmixing means mounted in the region of said bow for admixing andagitating water which passes beneath said bottom wall during cruisingmovement of said watercraft, said admixing means comprising an aperturedplate projecting forwardly from said bow in the direction of cruisingmovement of said watercraft at an upward angle of between substantially10* and 45*.
 62. In a watercraft, particularly a hydrofoil, incombination, an elongated hull of a predetermined first volume having abow and a bottom wall portion which is provided with a longitudinallyextending center keel; at least two stabilizing elements provideD onsaid bottom wall portion exteriorly of said hull and flanking saidcenter keel at opposite lateral sides thereof, said elements definingbetween themselves beneath and together with said bottom wall portion atleast one airchannel which extends longitudinally of said hull and has aseocnd volume of between substantially one-fifteenth and one-third ofsaid predetermined first volume; and admixing means mounted in theregion of said bow for admixing means comprising a grid-shaped admixingmember. and agitating water which passes beneath said bottom wall duringcruising movement of said watercraft, said admixing means comprising agrid-shaped admixing member.